Rolling magnesium alloy



Patented Jan. 2, 1934 UNITED STATES PATENT OFFICE ROLLING MAGNESIUM ALLOY Michigan No Drawing. Application February 2, 1933 Serial No. 654,880

9 Claims.

which contain relatively small amounts of alloying metals such as aluminum up to 8 per cent, manganese up to 2 per cent, cadmium up to 10 per cent, tin up to 8 per cent, zinc up to 3 per cent, the balance being not less than about 90 per cent magnesium.

Typical magnesium base alloys on which our invention may be practiced are those, for example, containing from 1 to 8 per cent of aluminum, from 1 to 0.1 per cent of manganese, the balance being magnesium. Such magnesium base alloys are among the strongest of those commercially available that possess a high resistance to corrosion. Accordingly, where strength combined with resistance to corrosion and the light weight characteristic of magnesium are prime considerations, these alloys are finding increasing usefulness for many purposes, particularly in the form of castings, forgings, and extruded shapes. Use of these alloys in rolled form to make sheet metal articles requiring forming operations such as bending, drawing and the like has not progressed to the same extent, inasmuch as it is usually necessary to heat commercially available sheet to elevated temperatures to permit making relatively sharp bends or deep draws without fracture. It is accordingly one of the objects of our invention to produce rolled sheet, plate, profiled shapes or the like of magnesium base alloys which possess a degree of ductility at ordinary temperatures permitting the same to be bent, cupped, or otherwise worked readily to a greater degree than hitherto possible without heating. We employ the term ductility to designate that quality of the metal by virtue of which such changes in shape may be made at room temperature without fracture. In obtaining numerical values for the ductility we employ a standard Olsen ductility testing machine in which the ball point is 0.875 inch diameter and the circular hole is 1.625 inches diameter. The depth of cup produced by cupping a specimen of sheet, for example, with this machine, is given herein as the measure of ductility. We have found that the minimum radius of a 180 cold bend which may be produced without fracture also gives a convenient measure of the ductility. In employing this test the radius is expressed in terms of the thickness of the specimen. I

In prior attempts to produce ductile magnesium alloy sheet the measurement of the percentage elongation of test bars thereof on being subjected to tension has been thought to represent the ductility, that is, the greater the percentage elongation the higher the apparent ductility of the product. .To produce rolled products possessing such elongation it has been proposed to carry out the rolling operations at temperatures from about 800 down to 500 or 400 F. and to make the finishing passes at the lower temperatures of the range. Following this rolling procedure, the metal is annealed. In testing this method we have found that, although the percentage 5 elongation may be increased thereby, the ductility may actually decrease; if not, it remains substantially the same.

We have discovered that in producing a magnesium base alloy rolled product a greater degree of ductility results if a relatively small cumulative reduction in thickness is made in the final stage of reduction at temperatures between about 40 and 350 R, such final reduction being preceded and followed by a suitable heat treatment, such as annealing. Thus it is suflicient for our purpose to produce the major part, e. g. approximately to 95 per cent, of the total reduction in thickness contemplated by conventional practice, anneal the metal, complete the reduction by roll- 30 ing at approximately room temperatures, and then re-anneal.

To the accomplishment of the foregoing and related ends, the invention, then, consists in the method hereinafter fully described and particus5 larly pointed out in the claims.

In carrying out our invention we may proceed in various ways depending upon the manner in which the first 80 to 95 per cent of the total reduction in thickness is produced. If we proceed according to conventional methods of rolling magnesium base alloys by repeatedly passing metal between the rolls of a mill at a temperature from 800 down to 500 or 400 F. so as to produce a reduction in thickness at each pass of 8 or 10 per cent, or whatever the metal will stand without fracture, and a cumulative reduction to approximately the final thickness, it is necessary to anneal the rolled product prior to carrying out the remaining operations. On the other hand, if the preliminary rolling or major part of the reduction is carried out at temperatures above about 600 R, which is the preferable procedure, we may eliminate the annealing step prior to the final operations, inasmuch as maintaining the metal at such temperatures, even though thesame is being rolled, produces the effect of annealing.

When it is desired to convert magnesium alloy sheet or rolled product produced in conventional l manner into a ductile product, it is advisable first to roll it at a temperature between approximately 600 and 800 F. in one or two light passes, producing a relatively small cumulative reduction amounting to a total of about 10 per cent of the metal thickness, so as to prepare the metal for the subsequent operations. This hot rolling has the eflect of annealing, so that simple annealing may in some cases be substituted for such hot rolling. Such annealing step consists in maintaining the metal at a temperature between about 600 and 800 F. for from to 2 hours or more. At the lower temperatures of the annealing range, a longer time is required than at the higher temperatures. We have found, however, that a sufficient amount of annealing is produced in approximately hour when the temperature is maintained between about 700 and 750 F.

We may proceed then with the final rolling at a temperature between 40 and 350 F. by repeatedly passing the metal between the rolls of a mill so as to produce a reduction in thickness of approximately 1 per cent or less per pass until the final thickness is attained. The amount of the cumulative reduction in thickness produced in this stage is limited by the condition of the metal or its ability to withstand a reduction without fracture and may be from about 5 to 15 per cent of the metal thickness, although a cumulative reduction of 10 per cent is preferable. The reduction may be made at any temperature within the range 40 to 350 F., already indicated, although it is convenient to roll' at room temperature (60-90 F.) or from room temperature up to 150 or 200 F. which temperatures may ordinarily be obtained without the need for preheating the metal owing to the heating effect of the rolling pressure. The maximum degree of improvement in ductility appears to be developed when the temperature is between 90 and 150 F.

The rolled product is then given a final annealing which consists in maintaining it at a temperature between about 500 and 800 F. for,

.to 2 hours or more, although about A; hour at 600 to 700 F. is usually suflicient.

The following examples are illustrative of preferable modes of carrying out the invention.

Example 1 A magnesium base alloy consisting of 4 per cent of aluminum, 0.3 per centof manganese, and the balance magnesium, was cast into an ingot and then extruded to form a rolling slab. The slab was rolled into sheet at temperatures between about 780 and 400 F. in a number of passes each producing up to 10 per cent reduction until the cumulative reduction in thickness was about 91 per cent. The sheet obtained was annealed for one hour at 750 F. At this stage specimens of the sheet which were about 0.136 inch thick, showed 10 per cent elongation in 2 inches, 0.104 inch Olsen ductility, and a minimum radius of bend of about six times the thickness of the sheet. The sheet was then rolled at room temperature in a series of passes producing about 1 per cent reduction in thickness per pass and a cumulative reduction of 9 per cent and then the sheet was annealed for two hours at 600 F. The annealed sheet which was about 0.121 inch thick showed 7 per cent elongation in 2 inches, 0.189 inch Olsen ductility, and a-minimum radius of bend of about three times the thickness of the sheet.

Example 2 A similar rolling slab was rolled into sheet about 0.121 inch thick at temperatures between 780 and 400 F. producing up to 10 per cent reduction in thickness per pass until the cumulative reduction in thickness was about per cent. The sheet was then rolled in two passes producing about 5 per cent reduction in thickness at a temperature between 700 and 600 F. reducing the thickness to about 0.110 inch. Specimens of the sheet showed 13.7 per cent elongation in 2 inches, 0.165 inch Olsen ductility, and a minimum radius of bend of about five times the thickness of the sheet. The sheet was then rolled at room temperature in a series of passes producing about 1 per cent reduction per pass and a cumulative reduction in thickness of 10 per cent and then the sheet was annealed for two hours at 600 F. The annealed sheet which was 0.050 inch thick showed 17.9 per cent elongation in 2 inches, 0.207 inch Olsen ductility, and a minimum radius of bend of about three times the thickness of the sheet.

Example 3 A similar rolling slab was rolled into sheet at temperatures between 780 and 600 F. in a number of passes producing up to 10 per cent reduction per pass until the cumulative reduction in thickness was about per cent and the thickness 0.137 inch. The sheet showed about 11 per cent elongation in 2 inches and 0.125 inch Olsen ductility. The sheet was rolled at room temperature in a series of passes producing about 1 per cent reduction in thickness per pass and a cumulative reduction of 10 per cent and then the sheet was annealed for 2 hours at 600 F. The annealed sheet which was about 0.122 inch thick showed about 17 per cent elongation in 2 inches and 0.195 inch Olsen ductility.

Example 4 A magnesium base alloy consisting of 4 per cent of cadmium, 1 percent of zinc, and the balance magnesium, was cast into an ingot and then extruded to form a rolling slab. The slab was rolled into sheet at a temperature between about 800 and 700 F. in a number of passes producing up to 10 per cent reduction per pass until the cumulative reduction in thickness was about 90 per cent and the thickness about 0.055 inch. The sheet obtained showed about 10 per cent elongation in 2 inches and 0.198 inch Olsen ductility. The sheet was then rolled at room temperature in a series of passes producing about 1 per cent reduction in thickness per pass and a cumulative reduction of 10 per cent and then the sheet was annealed for 2 hours at 600 F. The annealed sheet which was 0.050 inch thick showed 17 per cent elongation in 2 inches and 0.228 inch Olsen ductility.

Example 5 cent reduction per pass until the cumulative reduction in thickness was about 90 per cent and the thickness about 0.055 inch. The sheet obtained showed 13.6 per cent elongation in 2 inches and 0.140 inch Olsen ductility. The sheet was then rolled at room temperature producing about lper cent reduction in thickness per pass,

and cumulative reduction of 10 per cent and then the sheet was annealed for two hours at 600 F. The annealed sheet which was about 0.050 inch thick showed 14.5 per cent elongation in 2 inches and 0.180 inch Olsen ductility.

In the preceding examples, various combinations of steps are given by which the metal may be brought into a suitable condition whereby a limited reduction inthickness produced by rolling at room temperatures (60 to 90 F.) followed by annealing produces ductile sheet. Although a cumulative reduction of about 10 per cent produced by a number of passes at room temperature oi. about 1 per cent each is disclosed as operative, it is to be understood that the amount of reduction may be increased or decreased somewhat without departing from the spirit of the invention.

The use of the conventional methods of rolling and annealing in the preliminary operations to bring the metal to a thickness suitable for finish-rolling at a temperature between 40 and 350 F. is illustrated in Example 1. Therein the preliminary rolling was carried out at temperatures between 800 and 400 F., in conventional manner, and then the metal was annealed; fol-1 lowing which we added our novel steps, 1. e. low temperature (40 to 350 F.) rolling and flnal annealing. In this manner the ductility of the sheet was greatly improved as shown by the values obtained for these properties after cold rolling and annealing. Similar improvement over conventional practice is shown in Example 2, which diifers from Example 1 in that a relatively small amount of hot rolling is substituted for the first annealing step. In Examples 3, 4, and5, we have shown how ductile sheet or the like may be produced by employing but three steps, provided the preliminary rolling is conducted at a temperature above about 600 F.

Other modes of applying the principle of our invention may be employed instead of the one explained, change being made as regards the method and the steps herein disclosed, provided those stated by any of the following claims or their equivalent be employed.

We therefore particularly point out and distinctly claim as our invention:-

1. In a method of producing a ductile rolled product from a magnesium base alloy which has been previously rolled to approximately the final thickness at a temperature above about 600 F., the steps which consist in repeatedly passing said metal between the rolls of a mill at a temperature between 40 and 350 F. so as to produce a relatively small cumulative reduction in thickness, and annealing the rolled metal.

2. In a method of producing a ductile rolled product from a magnesium base alloy which has been previously rolled to approximately the flnal thickness at a temperature above about 400 F., thesteps which consist in annealing the said metal, repeatedly passing the same between the rolls of a mill at a temperature betwen 40 and 350 F. so as to produce a relatively small cumulative reduction in thickness, and annealing the rolled metal.

3. In a method of producing a ductile rolled product from a magnesium base alloy which has been previously rolled to approximately the final thickness at a temperature above about 400 F., who steps which consist in repeatedly passing said temperature between 800 and 600 F. and a rela-' tively small cumulative reduction at a temperature between 40 and 350 F., and annealing the rolled metal.

5. In a method of producing a ductile rolled product from a magnesium base alloy, the steps which consist in repeatedly passing said metal 'between the rolls of a mill so as to produce a major cumulative reduction in thickness at a the rolled metal, repeatedly passing the same between the rolls of a mill so as to produce a relatively small cumulative reduction at a temperature between 40 and 350 F., and annealing the rolled metal.

6. In a method of producing a ductile rolled product from a magnesium base alloy, the steps temperature between 800 and 400 F., annealing which consist in repeatedly passing said metal between the rolls of a mill so as to produce a major cumulative reduction in thickness at a temperature between 800 and 400 F., and a relatively small cumulative reduction at a temperature between 800 and 600 F., and a further relatively small cumulative reduction'at a temperature between 40 and 350 F.,

metal. 4

7. In a method of producing a ductile rolled product from a magnesium base alloy, the steps which consist in repeatedly passing said metal between the rolls of a mill so as to produce a major cumulative reduction in thickness at a temperature. between 800 and 400 F., annealing the rolled metal at a temperature between 600 and 800 F., repeatedly passing the annealed metal and annealing the rolled .between the rolls of a mill so as to produce a relatively small cumulative reduction at a temperature between 60 and 200 F., and annealing the rolled metal at a temperature between 500 1,25

and 800 F. Y

8.' In a method of producing a ductile rolled product from a magnesium base alloy, the steps which consist in repeatedly passing said metal between the rolls of a mill so as to produce a major cumulative reduction in thickness at a temperature between 800 and 600 F. and a relatively small cumulative reduction at a temperature between 60 and 200 F., and annealing the rolled metal at a temperature between 500 and 9. In a methodoi' producing a ductile rolled product from a magnesium base alloy, the steps which consist in repeatedly passing said metal between the rolls or a mill so as to produce a major cumulative reduction in thickness at a temperature between 800 and 400 F., a relatively small cumulative reduction at a temperature between 800 and 600 F., and a further relatively small cumulative reduction at a temperature between 60 and 200 F., and annealing the rolled metal at a temperature between 500 and800 F.

ROBERT D. LOWRY. FRED L. REYNOLDS. v 

